The present invention relates to an electrophotographic copying apparatus and more particularly to an electrophotographic copying apparatus capable of more easily detecting the cause of distortion in copied images.
In conventional electrophotographic copying apparatus, even if a document is properly set in place, distortion is sometimes caused in the copied images. By way of example, when the document shown in FIG. 8A is copied, the copied image is sometimes distorted as shown in FIG. 8B.
There are two causes for such distortion in the copied images. One cause is that the optical system is not properly adjusted and is distorted. More specifically, a mirror forming the optical system is deviated from its correct position. The optical system in an electrophotographic copying apparatus illuminates the document and exposes a photoreceptor by the light thus reflected to form electrostatic latent images. Therefore, if the optical system is distorted, normal electrostatic latent images cannot be formed, and thereby the copied images are caused to be distorted.
Another cause is that the copying paper is obliquely conveyed. When the copying paper, which is to be conveyed in parallel with a predetermined direction, is obliquely conveyed, the copied images on the copying paper are naturally distorted.
Conventional electrophotographic copying apparatus does not include a special mechanism for detecting whether the image distortion described above is caused by distortion of the optical system or by oblique transfer of the paper. For this reason, when servicemen adjust an electrophotographic copying apparatus in which the images are distorted to make the image normal, they need check both the optical system and the copying paper conveying mechanism.
If the electrophotographic copying apparatus has a reduction magnification function, the document is reduction-copied, and thereby the cause of distortion can be determined. For example, as shown in FIG. 9A, if the side edge of the reduction-copied document images is not parallel with the side of the copying paper so that a.noteq.b, it can be determined that the distortion is caused by the copying paper being conveyed obliquely. As shown in FIG. 9B, if the side edge of the reduction-copied document images is parallel with the side of the copying paper so that a=b, it can be determined that the distortion is caused by the optical system.
As mentioned above, servicemen can check both the optical system and the copying paper conveying mechanism, determine the cause of the distortion in the copied images, and adjust the electrophotographic copying apparatus to the normal condition.
However, if the electrophotographic copying apparatus has no reduction magnification function, both the optical system and the copying paper conveying mechanism should be checked actually, and it takes a lot of time to adjust the electrophotographic copying apparatus to the normal condition.
Further, if the electrophotographic copying apparatus has the reduction function, the cause of the distortion in copied images is determined using the reduction function thereof as mentioned above. However, to determine the cause accurately using the reduction function, the document is required to be rectangularly placed on a platen cover accurately. Accordingly, this work is laborious and takes a lot of time. If the reduction-magnification is set too small, the side edge of the document images is detached from that of the copying paper, and therefore it is difficult to decide whether they are mutually parallel. If the reduction-magnification is set too large (if it is nearly 1), the side edge of the document images is attached to that of the copying paper and it is also difficult to decide whether they are mutually parallel. In sum, the reduction-magnification is required to be adjusted to the most appropriate one. But this work takes a lot of time.